基于新监测指标的江南入梅早晚的气候特征及影响系统分析

Climate characteristics and influential systems of Meiyu to the south of the Yangtze River based on the new monitoring rules

中文关键词:  梅雨  入梅  气候特征  大气环流  海温异常

英文关键词:Meiyu  Meiyu onset date  Climatic characteristics  Atmospheric circulation  SSTA

中文摘要:

      利用中国气象局2014年发布的《梅雨监测业务规定》中的入梅日期资料、NCEP/NCAR再分析资料及NOAA海温资料等，重点研究了1951—2015年江南入梅早、晚的气候特征，及其与同期（5—6月）大气环流及前期海表温度变化的关系。结果表明，近65年来江南入梅日具有显著的年际变化特征，入梅平均日期为6月8日，最早和最晚相差47 d。入梅日主要出现在6月，占80.0%。江南入梅偏早和偏晚年，对流层高层至低层的同期大尺度环流存在明显的差异。入梅偏早年，高层南亚高压和东亚副热带西风急流（西风急流）的建立较早，强度较强，南亚高压北移到青藏高原上空亦偏早，西风急流北跳偏早；中层中高纬度经向环流较强，而西北太平洋副热带高压（副高）第1次北跳偏早；低层索马里越赤道气流建立较早，强度较强，西太平洋为反气旋式距平环流；入梅偏晚年上述环流系统演变特征则基本相反。冬、春季海表温度的异常是影响入梅早、晚的重要的外部强迫因子，也是重要的前期预测信号：当冬季东太平洋海表温度为负距平、澳大利亚东部海表温度偶极子为正位相及春季北大西洋三极子处于正位相时，江南入梅偏早；上一年12月澳大利亚东侧海表温度偶极子和当年3月北大西洋三极子与江南入梅早、晚关系最为密切，当12月澳大利亚东部海表温度偶极子为正位相时，副高第1次北跳偏早，当3月北大西洋三极子为正位相时，6月西风急流偏强、偏北，有利于江南入梅偏早。

英文摘要:

      Using the NCEP/NCAR reanalysis data, NOAA Sea Surface Temperature (SST) data, the Chinese Meiyu onset dates determined based on "Meiyu Monitoring Business Rules" released by China Meteorological Administration in 2014, and other data from 1951-2015, anomalous climate characteristics of the Meiyu onset date in three regions of South China are analyzed. The relationships between the Meiyu onset date to the south of the Yangtze River (MODSYR) with variations of atmospheric circulation in May-June and preceding SST are analyzed using the correlation and composition analysis methods. The results show that MODSYR has significant interannual variability in the recent 65 years. The mean MODSYR during 1951-2015 was on 8 June. The difference between the earliest and the latest MODSYR was 47 days. The MODSYR was usually in June (accounting for 80.0%). There exist significant differences in the large-scale circulation from the upper troposphere to the lower troposphere during the same period (May to June) between the earlier and later MODSYR years. In the early MODSYR years, the South Asia high (SAH) and East Asia subtropical westerly jet stream (SWJS) establish earlier and are stronger compared with their climatological means in the upper troposphere, the SAH moves northward to the Tibetan Plateau earlier than normal, and the SWJS also moves northward earlier. The mid-and high-latitudes is dominated by strong meridional circulation, and the first northward jump of the western Pacific subtropical high (WPSH) occurs earlier than normal. The cross-equatorial flow in the lower troposphere establishes earlier, and the onset of the South China Sea summer monsoon is earlier, too. However, the opposite is true for late MODSYR years. SST anomalies (SSTA) in the preceding winter and spring are important forcing factors that affect the MODSYR, and they are also critical early predictive signals. When the eastern Pacific SSTA is abnormally cold in the preceding winter, the SST gradient index to the East Australia (ASI) is in positive phase to the East of Australia and the spring North Atlantic Triassic (NAT) is in the positive phase, the MODSYR is earlier than normal. The relationship between the December ASI, the March NAT and MODSYR are the closest. When the December ASI is in positive phase, the first northward jump of the WPSH occurs earlier than normal. When the NAT is on positive phase in March, the SWJS will be stronger and located more northward in June, which is favorable for earlier MODSYR.